This invention relates to a chair, or sitting furniture, particularly one for children or teenagers, which comprises a seat, a back-rest, a supporting frame resting on the floor via approximately horizontal base legs, a support arm mounted on the supporting frame and a horizontal shaft secured to the support arm in the area of the seat designated for knee support; further, it comprises a pivotable seat support member connected to the support arm by means of the shaft, and a spring mechanism secured to the arm and to the seat support member, the support mechanism being adapted to suppress the pivotal motion of the seat support member when its angle of tilting, as limited by detents decreases, and to stimulate the pivotal motion when the angle increases.
In a known chair of the above discussed type (Swiss Pat. No. 592 429) the spring is an auxiliary means for adjusting the inclination of the seat as desired, the inclination being fixed by means of a device locks the tiltable seat support member with the non-tiltable support arm. While the inclination is adjusted, the seat tilts in one direction due to the user weight and in the other direction due to the return action of a pneumatic spring, the casing of which is pivotably secured to the supporting frame at the lower end and to the seat support member at the upper end. The pivot axis being situated in the direct vicinity of the knee-support area of the seat has the advantage that even in case of a stronger tilting of the seat, the user's feet are not lifted from the floor. The seat angle can be fixed in a selected position by means of the pneumatic spring.
It is also known, in a chair without the provision of a variable seat inclination, to install a helical spring substantially horizontally between the seat support member and the support arm so that the user can sit down relatively "softly" as the seat support member is brought to rest on the arm when the helical spring is compressed to its maximum. It is possible to provide a gradual progression of the springing action through a variable pre-stress setting of the compressed spring (German GM No. 84 01 116.5=German Pat. No. 34 01 314.8). From the same specification (embodiment of FIGS. 7-10) it is also known to substitute the pivot shaft by a pre-stressable torsion bar whereby a limited pivotal motion of the seat support member against the support arm is permitted. The torsion bar suppresses the tilting of the seat support member when the pivot angle decreases and stimulates the tilting when the angle increases. It should be noted that the characteristic curve of a reasonably priced torsion bar is strongly progressive. Therefore, when the user is seated, only very restricted rocking motion through an active displacement of the centre of gravity, i.e., a further decrease of the pivot angle is possible, which essentially holds true for springs with strongly progressive characteristic curves. (see torsion bars in German AS No. 1429404 and German OS No. 1943633).
The object of the invention is to provide a chair of the above discussed art without considerable additional technical input, such that the user, on one hand, can effect a substantial tilting of the seat by relatively small displacement of the centre of gravity, and, on the other hand, involuntary tilting is avoided to a large degree wherein such a tilting motion corresponds to a rocking motion and thereby, the natural restlessness of a young chair user is taken into account.